There's always WINE. It's supposed to work on OS X as well. Takes care of the issues with drive space and rebooting. If you have the drive space, you can also use virtual machine/virtualization software. I think Parallels Desktop lets you launch Windows apps like native programs in OS X.

The quality of WINE depends on what programs you use. Some programs run flawlessly, others not so much. This is true even on Linux. There's a compatibility list online, but you won't find obscure programs like the GC Image Rebuilder.

As far as i can see the GC Image Rebuilder uses dotnet3.5 framework which has limited functionality in Wine.
It might run in mono tho, but I haven't tried.

Wine does work very well on OSX, but Wine needs quite some configuration for many apps/games which can make it seems hard when you start using it.

By the way, if you use latest versions of OSX (10.8.2 or 10.7.5), be sure to update your X server, because there was a bug in previously released X servers in OSX which breaks compatibility with 10.8.2 and 10.7.5.

There is however one huge issue in relation to OSX and Wine, and that only affects AMD cards.
The AMD drivers for OSX reports the wrong numbers of MAX_VERTEX_UNIFORM_COMPONENTS, which kills performance in certain games. This can however be resolved by patching Wine with setting this as a specific value instead of getting it from the drivers.